Pull ribbon for snap action vane switch



Jan. 30, 1962 J. w. WELSH 3,019,318

PULL RIBBON FOR SNAP ACTION VANE SWITCH Filed Jan. 29, 1960 FIG. e.' FIG. 7. r

30 OxlnlzED CARBON FILM gqqfgfgj CARBON HLM n." man... u

v. n... r c

6oF G l0 I lNvENToR JAMES W. WELSH AT TORNEYS.

ping of the vane.

n automotive vehicle.

United States Patent Oiilice 3,019,3l8 Patented Jan. 30, 1962 York Filed Jan. 29, 1960, Ser. No. 5,512 13 Claims. (Cl. 200-1Z2) This invention relates to snap action vane types of electric switches in which the vane is normally constrained to a stress-deformed condition by a heat 'expansible pull element secured at its ends to the vane, with the vane snapping to another position upon expansion of the pull member. More particularly, the invention is directed to a novel means for concentrating the heating effect at one selected location of the pull member or pull strip' to thereby achieve more uniform operationof the switch throughout its operating life.

In prior U.S. patents issued toD me, I have shown and described a novell type of snap action vane comprising a substantially at piece of resilient material having a substantially rectilinear deformation extending thereacross, preferably along'a diagonal thereof in the case of a square vane, the deformation being interrupted intermediate its ends to leave the central portion of the vane free of deformation. Such a vane thus assumes an initial restored position in which it is bent about the deformation. For use in a snap action electric switch, this Vane is constrained to bend about a line which is substantially perpendicular to the deformation' by attaching a heat expansible pull element to the vane, the pull element having its ends attached to the vaney adjacent the ends of the deformation and extending parallel to the latter. cool or contracted* condition so that it normally constrains the vane to be bent to a stress-deformed condition. When the pullielement is suiiiciently heated to expand enough to release the bending stresses in the vane, the vane snaps to a restored position in which it is bent about the line of the deformation.

If such a vane has a mounting'element, such as a mounting bracket, secured thereto at a mounting point spaced laterally of the deformation, the vane thus being fixed against movement at suchmounting point, the free portion of the vane will have a relatively large amplitude of movement relative to the mounting point during snap- Also, the pull element willr move `toward and away from the vane during the snapping of the latter.

These movements of the free yportion of the vane and of the pull member, relative to each other and relative to the fixed mounting point of the vane, may be utilized by novel circuitry to provide electric snap action switches for controlling, for example, the signalling circuits of an The snap action vane usually has associated therewith a pull element which is of a material of ahigh electrical resistance and which is heated by passage of electric current therethrough. When so heated, thepull element expands and, when the electric circuit is interrupted, the pull element contracts. However, for proper operation, the length of the pull element must be very carefully selected in order to conform to the switch parameters. Otherwise, a ballast resistance must be used in series with the pull element. This is a disadvantage, particularly where a relatively short length of the pull element is desired.

ln my U.S. Patent No. 2,706,228, issued April 12,

' 1955, l have shown and described pull element constructions in which these disadvantages can be eliminated.

" More specifically, the thermally expansive pull element This pull element is attached to the vanefin its .perature.

is indirectly heated by a high resistance wire operatively associated therewith. In such case, the length of the pull element does not have to be determined yby the amount of the resistance desired to be used, and the amount of resistance vwire is not dependent upon the length of the pull element. Consequently, a snap action switch can be provided embodying a pull element of any desired length and independent of the heating resistance of any desired value.

The switch of my said patent is very satisfactory in operation. However, it has been found that the operating characteristics thereof will change, over an extended period of use, due to creep caused by the stressing of the pull element under conditions of relatively high tem- While this condition has been retarded to a certain degree by using diiferent high temperature alloys, complete elimination of the creep problem has not been `effected as a practical matter.

In laccordance lwith'the present invention, the foregoing diiiculties are avoided by concentrating the heat input to the pull element or pull member at one point or very short Zone along the latter so that only this point or zone is heated to any appreciable extent and the remaining portions of the pull member remain in a relatively cool condition. By concentrating the heat at a local area along the pull element, the heating characteristics can be accurately controlled during life of the asher. Additionally, as the heating is no longer distributed throughout the length of the pull element, there is no cumulative effect of incremental changes along the length of the pull element. The entire ilasher operates under much cooler conditions, due to the concentration of the heat at only such local areas.

kWhile various arrangements may be made for concentrating the heat, it has been found that the best results are obtained when the current input to the pull member is applied thereto through a carbon pile resistance. This resistance may be a piece of either of glass or cloth tape impregnated with carbon and wrapped around the pull member, the tape being impregnated with adhesive on both sides, or may be provided by painting of carbon material onto the pull element by spraying or dipping, oxidizing carbon material onto the pull element,rapping ya tape or the like impregnated with carbon around the pull element and securing it in position by twisting a -wire therearound, riveting the carbon tape or the like to the pull element, or molding a piece of carbon or graphite with an aperture molded to the pull ribbon and an aperture molded to the current lead.

For an understanding of the invention principles, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings. In the drawings:

FIG.k lis a side elevation of one embodiment of a thermostatic pull strip incorporating the invention.

FIG. 2 is a sectional view taken on the line 2--2 of FIG. l.

FIG. 3 is a perspective view of a normally closed snap action switch embodying the invention, schematically in dicating the external circuit connections.

FIG. 4 is a sectional view on the line 4--4 of FIG. 3.

FIGS. 5 through l0 are views, similar to FIG. 2, illustrating modied forms of the invention.

Referring to FIGS. l through 4, a snap action vane 10, of the type described above, is illustrated therein and is preferably made of relatively thin spring metal, with consideration being given to its spring factor, stiffness, temperature co-eflicient, and the like, in accordance with the desired rate of operation of the snap action. As the construction and general characteristics of vane 10 have been fully described in my issued patent, it is not believed that it would be useful to repeat such description at this point. However, it may be stated briefly that the vane lil is deformed along a diagonal in two elongated spaced portions or bosses l5 and initially has a bend about the line of these deformations, this initial bend being hereinafter referred to as the restored position of vane lll. For use in a snap action switch, the vane is bent into a deformed position forming another shallow V along the diagonal 16-17, by applying bending forces at the outer ends of the deformations l5. When the forces at the outer ends of these deformations are released, or overbalanced by kinetic energy stored in vane i9, the vane snaps back to a position bent along the deformations l5. The vane is supported by a relatively rigid electrically conductive mounting member or bracket Ztl which is attached to vane itl laterally of the deformations 'and formed a fixed pivot point for the vane during the snap action of t-he latter.

In accordance with the invention, an indirectly heated, heat expansible element at), of conductive metal, is secured, in contracted relation, to the corners ll and l2 of vane l0. The attachment may be made, for example, by soldering, brazing, or spot welding the ends of element 40 to the vane, and is effected while the vane is stressdeformed about the diagonal 16--17 and while element 40 is in the cooled and contracted condition. Thereby, when element 4t) is heated and expanded la pre-determined amount, the kinetic energy stored in vane 10 will overbalance thetension of element 40 and snap the vane to its restored position in which it is bent about the diagonal 11-12.

The indirect heating is effected by operatively associating a preferably insulated high resistance Wire 3th with element 4t). The length of the wire Sil is independent of the length of element 40 and the parameters of vane 1t). and is conditioned solely by the amount of resistance it is necessary or desirable to include in the heating circuit for the vane operator dil. lIn the illustrated examples, element '40 is a channel shaped strip having resistance wire 30 extending therethrough and with its ends brought out of the channel at selected points in accordance with the desired switch contact and circuit arrangements.

Referring more particularly to FIGS. 3 and 4, bracket Ztl has one end secured to the same surface of vane l()1 as has the strip dit therealong. The central or intermediate section 22 of bracket 20 carries a dielectric wrapping 23 around which is a conductive band 24 carrying a contact 25 facing electrically conductive strip 4Q, The latter has secured thereto, in a manner described more fully hereinafter, a contact 35 engaged with contact 25 in the stressdeformed condition of vane l0 with strip #lil contracted. High resistance wire has one end connected to band 24, and thus to contact 2S, and its other end connected to a grounded lamp 55. A grounded battery 56 is connected, through a control switch 37, to the end 21 of bracket Ztl.

In the position of the parts shown, when switch 37 is closed, current flows from battery 56 through switch 37, bracket 20, vane 1t), strip 4t) from both ends thereof, Contact 35, 4contact 25, band 24 and lamp 55 to ground. The current flow through wire 30 rapidly heats the latter to a high temperature, thus heating the embracing channel strip `40. The resistance of the latter is so small that the heating effect of current flowing therethrough is negligible. As strip 40 is heated by wire 3), it expands and, after preset expansion thereof, vane 10 is released to snap to its restored position. As strip 40 is thus pulled toward vane 10 `and away from bracket 20, contacts 25, 35 are snapped open, breaking the energizing circuit for wire 30. The latter and strip 4i) now cool. As strip 40 contracts towards its illustrated position, vane 10 is snapped to the stressdeformed condition, closing contacts 25, to repeat the cycle.

In accordance with the present invention, the current ow into element is provided through a carbon pile resistance. Thus, and as illustrated more particularly in FIG. l, a glass or cloth tape 6i) impregnated with carbon is wrapped around element 40 and is held thereon by a metal band 61 crimped over the tape. As a result of this construction, the heating effect of the current is substantially all concentrated at the area of element 40 contacted by the tape impregnated with carbon, indicated at 69, and the remainder of the pull strip is heated Very little if at all. As stated, this concentration of the heating effect results in better long time operation of the pull member Without the change in characteristics due to creep `and the like.

In the embodiment of FIG. 5, a glass or cloth tape 60A impregnated with carbon has adhesive 62 on one or both surfaces. Thereby the tape may be adhered to the pull element 40 and have a metal band 61A crimp therearound or adhesively held against the outer surface of tape 60A. The arrangements operates the same as that indicated in FIG. 2 and -as described herein as above.

In the embodiment shown in FIG. 6, a film of carbon 60B is painted onto element 40 and a band 61B is crimped around the element 40 over the painted film 60B.

FIG. 7 illustrates a somewhat similar arrangement in which an oxidized carbon film 60C is applied to the outer surface of element 40 at a local area thereof and a band 61C is crimped around and over the film 60C.

In FIG. 8, a tape 60D essentially identical with tape 60 of FIG. 2 is wrapped around pull element 40 at a local area thereof and is compressed against the element 4t) by a wire 61D or the like which is twisted around the tape. This combination works in the same manner as described for the other modifications, with the resistance being held under pressure to the pull ribbon. When the carbon mateiial is` used in the manner of FIG. 8, the pressure exerted thereagainst can be used as an adjustment for the speed of operation.

In the embodiment of FIG. 9, a tape, impregnated with carbon, is indicated at 60E as held to pull element 40, along with band or conductor 61E, by a rivet 63. In this modification, two separate pieces of tape could be used, one beneath the lower head of rivet 63 and the other beneath the ribbon 61E.

In the embodiment of FIG. 10, a molded piece of carbon 60F is apertured to slip over the element 40, and also apertured to receive a conductor or ribbon 61F. Preferably, in this case, the molded carbon 60F is molded directly to the pull element 40 and to the conductor 61F.

In each of the cases, the bulk of the carbon must be kept sufficiently small that it will not interfere with proper operation of the pull ribbon. lUnits made with this carbon type resistor conducting cuirent into the pull element are so cold in operation that there is practically no possibility that creep will be experienced under any elevated temperatures.

While specific embodiments of the invention have been shown and `described in `detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

l. In a snap action electric switch, a snap action vane normally bent to a` restored position about a rst line thereacross; a heat-exp-ansible, electrically conductive pull element secured in the cold and contracted condition, to the vane at the outer ends of said rst line to bend the vane into a stress-deformed position about a second line substantially perpendicular to said first line, said vane, upon expansion of said pull element, snapping to its restored position; meansmounting said vane at a fixed pivot point spaced laterally of said first line to provide a vane free portion having a relatively large amplitude of movement relative to said pivot point; said pull element, during snapping of said vane, having a relatively large amplitude of movement relative to said pivot point;

Van electric heating circuit for said pull element, including a first contact carried thereby and engaging a second contact, fixed relative to said pivot point, when the vane -is in its stress-deformed position; and a layer of high-resistance carbonaceous material covering a localized area of said pull element, said rst contact being in mechanical engagement with the outer surface of said layer and electrically connected to said pull element only through said layer; whereby due to such high-resistance carbonaceous material, the electric current heating effect is substantially all concentrated in such localized area of said pull element; said heating circuit including a highresistance electric wire in transfer relation with said pull element.

2. A snap action electric switch as claimed in claim l in which said carbonaceous layer is constituted by a lexible tape, impregnated with carbon, and wrapped around said pull element; and said tirst contact includes a metal band crimped around said tape and clamping the same to said pull element.

3. A snap action electric switch as claimed in claim 2 in which the ilexible material of said tape is cloth.

4. A snap action electric switch as claimed in claim 2 in which said flexible material of said tape is glass.

5. A snap action electric switch as claimed in claim 1 in which said layer of carbonaceous material is constituted by a flexible tape impregnated with carbon and having a coating of adhesive on one surface by means of which the tape is adhered to said element; and said first contact includes a metal band extending around the outer surface of said tape.

6. A snap action electric switch as claimed in claim 5 in which said tape has -a layer of adhesive on both surfaces, whereby thek metal band is adhered to a surface of said tape.

7. A snap action electric switch as claimed in claim 1 in which said layer of carbonaceous material is constituted by a carbon ilm painted on the outer surface of said pull element; and said rst contact includes a metal band crimped around said pull element in contact with said iilm.

8. A snap action electric switch as claimed in claim 1 in which said layer of carbonaceous material is constituted by a lm of oxidized carbon on the outer surface of said pull element; and said first contact includes a metal kband crimped around said pull element in contact with said lm.

9. A snap action electric switch as claimed in claim k1 including electrically conductive means holding said carbonaceous material in pressure engagement with said pull element.

l0. A snap action electric switch as claimed in claim 9 in which said layer of carbonaceous material comprises a ileXible tape impregnated with carbon; and said first contact comprises a wire twisted around said tape and holding the same in contact with said pull element.

11. A snap action electric switch as claimed in claim l in which said layer of carbonaceous material is constituted by ka exible tape impregnated with carbon and wrapped around said pull element; said first contact includes a metal strip; and a rivet extending through said strip and said layer and holding said strip engaged with said layer and said layer engaged with said pull element.

12. A snap actio-n electric switch as claimed in claim 1y in which said layer of carbonaceous material comprises a pair of strips of exible material impregnated with carbon disposed on opposite sides of said pull element; said first contact includes a metal band; and a rivet extending .through said band, said strips, and said element, and holding said band against one of said strips and both of said strips against said element.

13. A snap action electric switch as claimed in claim 1 in which said layer of carbonaceous material is constituted by carbon molded about said pull element and about a metal strip constituting said iirst contact.

References Cited in the ile of this patent UNITED STATES PATENTS 1,832,419 Pender Nov. 17, 1931 2,806,921 Welsh Sept. 17, 1957 2,907,850 Colombo Oct. 6, 1959 

